Q1, Enable the terrestrial tuner in T2 mode. Region is not relevant to ABM scanning. ABM is the quickest way to achieve this as long as the mast is available in the list and any overrides for T2 are current. If not create a new provider with "DVB-T frequency finder".
Q2, Signal finder is nothing to do with ABM. Use "DVB-T frequency finder" to create an ABM provider. The new provider persists through config file and OpenViX updates and is also saved by OpenViX backups.
Q3, If Burnham-on-Crouch is a repeater of Sudbury there would be no bonus in receiving anything from Sudbury. If Burnham-on-Crouch transmitter is not included in ABM list use "DVB-T frequency finder" to create it. I am not going to repeat how in this thread because it is explained in the ABM sticky.
Q4, No idea. I don't live in the UK. As far as I know COM7 and COM8 is identical across the 4 nations. Local muxes would have different TSIDs. Use "DVB-T frequency finder" to create a provider. The "home transponder" of the provider will be the strongest DVB-T mux. The only TSIDs used to create the bouquet will be the ones listed in the SI tables on that mux.
Q5, The frequency with the strongest signal for each TsId found. TerrestrialScan does not create anything for ABM. "DVB-T frequency finder" only creates ABM files.
Q6, A frequency change will only affect ABM if the home transponder changes frequency or one of the T2 muxes changes frequency. Creating a new provider with "DVB-T frequency finder" will cure this. If channel names ever change they will be automatically updated by enigma (unless this feature has been overridden).
Q7, LCN values are read from the transport stream of the home transponder. As the LCNs come from the transport stream there is no wait for anything.